What does an Electroretinogram show?
Definition. The electroretinogram (ERG) is a diagnostic test that measures the electrical activity of the retina in response to a light stimulus. The ERG arises from currents generated directly by retinal neurons in combination with contributions from retinal glia.
Where is the ground electrodes placed in ERG?
The standard ERG setup includes several electrodes. Typically a reference electrode is placed on the skin in the middle of the forehead. Grounding electrodes for each eye are placed on the earlobes.
Is ERG derived from cornea?
The major components of an ERG signal are the cornea-negative a-wave and the cornea-positive b-wave. The a-wave is derived from the cones and rods of the outer photoreceptor layers and the b-wave reflects post-synaptic bipolar and Muller cell activity, in turn driven by photoreceptor input26.
What is a wave in ERG?
The waves are called a-, b- and c-waves. An additional corneal-positive wave, that is more rarely recorded at the termination of the light flash, is called the d-wave. Figure 1 shows ERG responses from different species. These responses are to bright light stimuli applied in the dark-adapted state.
Is electroretinography painful?
Electroretinography (ERG) Responses to flashes of light are measured via electrodes placed on the surface of the eye. It is a painless test.
What are A and B waves in ERG?
The a-wave, sometimes called the “late receptor potential,” reflects the general physiological health of the photoreceptors in the outer retina. In contrast, the b-wave reflects the health of the inner layers of the retina, including the ON bipolar cells and the Muller cells (Miller and Dowling, 1970).
Why ERG test is done?
Why do I need an electroretinography test? Your doctor may perform an ERG to determine if you have an inherited or acquired disorder of the retina, such as: retinitis pigmentosa, which is a genetic disease causing loss of peripheral and night vision.
How long does an Electroretinogram take?
The standard ERG typically takes about an hour. For the dark-adapted portion of the test, the patient sits in the dark for 20 minutes. Dim light flashes that gradually increase in brightness then appear and the retinal responses recorded. This part takes another 10 to 15 minutes.
Why do a person needs an electroretinography test?